In a typical telecommunications network based on wire cable, the switching nodes (e.g., central offices) are interconnected using a dedicated mesh architecture with limited switching. This means that there is a dedicated wire cable link extending between each pair of nodes in the network.
With the introduction into the network of optical communications technology including single mode optical fibers, a more efficient, flexible and economical utilization of the relatively large available bandwidth can be achieved using a central hub architecture. In such a hub architecture, each of the switching nodes or central offices is connected to a central hub switch by means of an optical fiber link.
Generally, the hub switch itself is an electronic switch. Thus optical signals are transmitted to the hub switch via the optical fibers and are converted from optical to electronic form for processing in the hub switch. The signals processed in the hub switch are then reconverted back to optical form for transmission out of the hub switch. Because of inherent switching speed limitations characteristic of the electronic switching devices comprising an electronic hub switch, current electronic hub switches cannot process incoming data channels at rates faster than a few hundred megabits per second. This is only a fraction of the bandwidth that is required for the broad band applications, such as high definition video and interactive data communications, presently under contemplation for telecommunications networks. Such applications are expected to require data throughputs at individual subscriber stations in excess of 100 Gigabits per second and communications between switching nodes or central offices are expected to require data throughputs in the Terabit per second range.
Accordingly, efforts have been directed toward the development of optical telecommunications networks which utilize an optical central hub instead of an electronic central hub. An optical central hub provides the needed high data throughputs and eliminates the need for conversion of data from optical to electronic form and reconversion back to optical form.
Examples of such all optical networks are described in Cheung-Kobrinski-Loh U.S. patent application Ser. No. 948,244, entitled "Multiwavelength Optical Telecommunication System," filed Dec. 31, 1986 and now abandoned and Arthurs-Goodman-Kobrinski-Vecchi U.S. patent application Ser. No. 046,912 entitled "Optical Cross-Connect for Parallel Processing Computers" filed on May 6, 1987. Both applications are assigned to the assignee hereof. The Cheung-Kobrinski-Loh patent application describes a network in which each node has a transmitting system capable of transmitting radiation at a unique wavelength associated with the particular node. Each node also has a receiving system capable of receiving all of the wavelengths produced by the various transmitting systems in the network. A passive central optical hub element is adapted to receive radiation over optical fiber links at a different wavelength from each of the transmitting systems. The central hub element also transmits over optical fiber links a fraction of the power received at each wavelength to all receiving systems. Thus, each node receives a fraction of the power transmitted by every other node. The receiving system at each node is tunable to a given one of the wavelengths transmitted thereto so that communications between pairs of nodes in the network can be achieved. Illustratively, each receiving system may comprise a tunable optical heterodyne receiver. Alternatively, each receiving system may comprise a wavelength division demultiplexer for separating the arriving wavelengths and a dedicated detector for each wavelength. A control system is provided for selectively activating one of the detectors.
The above-described network is especially suitable for applications such as wideband broadcasting and multicasting services and for the setting up and tearing down of wideband virtual connections. However, the above-described network is not particularly well suited for the establishment of very high capacity (e.g., total throughput in the Terabit/sec range) dedicated point-to-point connections between particular pairs of nodes. In particular, a hub element capable of transmitting a fraction of the power from each transmitting system to all receiving systems and receiving systems capable of tuning to a selected wavelength represent an unneeded investment in network hardware when the objective is to provide very high capacity dedicated point-to-point connections between nodes.
One network architecture which is suited for providing very high capacity dedicated point-to-point connections is an optical mesh architecture in which there is a dedicated optical fiber link between each pair of nodes in the network. However, such a mesh architecture requires a massive deployment of optical fibers and in addition such a mesh architecture cannot be provided by upgrading presently in place optical fiber networks based on electronic hub switches.
In view of the above, it is an object of the present invention to provide an optical network architecture suitable for providing dedicated very high capacity point-to-point connections. More particularly, it is an object of the invention to provide an optical network architecture suitable for providing dedicated point-to-point connections with data transmission capabilities in the Terabit/sec range and suitable for broad bandwidth services such as high definition video and interactive data communications. It is a further object of the present invention to provide such dedicated high bit rate point-to-point connections by way of a hub topology so that the fiber links in already existing optical hub networks can be utilized and no massive deployment of optical fibers is required.